Study conjoins MRLS, pericarditis

Lexington, Ky.-While mare reproductive loss syndrome (MRLS) was swiftly becoming a household word in Kentucky last spring, animal practitioners in central Kentucky were also reporting an influx in the number of cases of pericarditis, an uncommon disease involving the heart and the sac around the heart.

As researchers scrambled to determine a cause for MRLS, questions abounded as to whether the syndrome and pericarditis were linked.

A recently completed study provided scientific evidence confirming a relation between MRLS (which included early fetal loss and late-term abortions) and the pericarditis cases.

"These both occurred at the same time and both in such large numbers," says Dr. Nathan Slovis of Hagyard-Davidson-McGee, who collected data for the study. "We can say MRLS and pericarditis in Kentucky this spring were related; they might not be brother and sister, but they certainly are cousins. They have to share at least some of the factors with MRLS.

"We all believe this (pericarditis) is a multi-factoral disease," he tells DVM Newsmagazine. "It isn't just one toxin that occurred."

Data for the study was also collected by Lexington-based Dr. Johanna Reimer of Rood and Riddle Equine Hospital, and then analyzed by a group headed by Dr. Noah Cohen of Texas A&M University. Other team members included Drs. Vincent Carey, James Donahue, Janyce Seahorn, Chris Smith and Shelly Lenz.

The study analyzed 38 affected horses and 30 control horses. Researchers point out that the small sample size can limit the statistical power to detect differences and to note effects of multiple exposures simultaneously.

But according to Cohen, "Confounding can occur in studies of populations of any size-large or small. In our pericarditis study, after accounting for effects of caterpillars, many of the associations (pond water, cattle) disappeared; this may have been due to confounding, but also might have been attributable in part to small sample size."

Some statistical study points:

The proportion of cases of pericarditis that were from farms where there were mares or foals affected by MRLS (84 percent) was significantly greater than that of the controls (56 percent).

There was a significant association of pericarditis with reported exposure to caterpillars.

Caterpillars, but not cherry trees, were associated with the development of pericarditis.

Pericarditis cases were less likely to have access to pond water (5 percent) than controls (23 percent), indicating an association with management or water source that may have been protective.

Slovis says some of the findings surprised him, such as the pond water, but not all.

An example of fibrinous pericarditis

"As for the aspect in regard to cherry trees. That didn't surprise me too much. These animals didn't appear to be exposed to cherry trees like everybody kept harping on with the mare reproductive loss syndrome," he says.

"These findings are markers for the real thing," he says. "We need to find out why were these people, for example, bringing in hay from outside Kentucky (at least for pericarditis). These are clues to what really caused this. These raise your brow as to what is going on."

A larger study by the same group of epidemiologists is under way to look at early fetal loss and late-term abortions to see if there are any correlations with the pericarditis study.

Slovis says this study is expected to be completed within the next two months.

For now, the cause for MRLS is still not conclusive, says Slovis. "I know they're saying cyanide is big. That's hanging on by a loose thread. There are a lot of other factors that we need to see."